This invention relates to means for attaching a corona filament wire to a terminal strip easily and without the use of fasteners.
Corona discharge devices are frequently used in electrostatic copying apparatus. In such apparatus, a sheet of copy paper is provided with a coating of a photoconductive insulating material and passed through a corona charging device which imparts a substantially uniform electrostatic charge to the coated side of the paper. The paper is then subjected to a light pattern image or indicia on the original document whereupon the electrostatic charge is dissipated in the light non-image areas but is retained in the darker image areas after which the sheet is subjected to an application of electrostatically attractable toner particles to develop the latent image left on the paper.
Substantially the same principles are applied in the field of reusable electrostatic copying in which the photoconductive insulating material is a coating on a drum or a belt which is grounded and on which the latent electrostatic image is formed and developed. This image is then transferred to ordinary paper, and the drum or belt cleaned and reused in the same manner to make successive copies.
In either of the foregoing processes, it is necessary to electrostatically charge the photoconductor prior to exposing it to the light pattern. This is done by means of corona discharge from one or more very thin filaments or wires on the order of from 2 to 3 mils in diameter which are stretched across the path of the photoconductor and to which is applied a negative electric potential of the order of 6,000 volts.
Corona filaments are also used in various other aspects of copying such as the application of a bias voltage during developing, transfer of the image or cleaning of the photoconductor.
A principal problem with the corona discharge apparatus is the accumulation of dirt and other foreign matter on the corona wire. It is known that accumulations of dirt, such for example as paper dust, dry toner particles, etc. prevent a corona effect from being achieved along the portion of the wire which is covered by the foreign matter. Thicknesses of as little of 2 mils of foreign matter on the corona discharge wire have been found to be sufficient to prevent the corona from being produced along that portion of the wire. This results in a nonuniform electrostatic discharge on the photoconductor, and therefore, in the case of a charging corona, for example, any image projected on this portion of the photoconductor is not reproduced since no toner particles will adhere to a noncharged area of the photoconductor.
While it is possible initially to clean dirty corona wires manually with a soft brush, once the deposits have been allowed to collect and congeal, this is not very practical since the wires are delicate and easily broken if anything more than the lightest force is applied.
The most effective way of handling the problem of a corona discharge wire to which foreign deposits have become firmly attached is to replace the wire entirely. The present invention provides an improved system and apparatus for facilitating replacement of the corona discharge wire. Reference may be had to the prior patents to Martin U.S. Pat. No. 3,499,143 and to Salger U.S. Pat. No. 3,566,223 for prior art teachings directed to the replacement of corona discharge wires.
The present invention provides an improved filament assembly wherein the corona discharge filament can be put in place merely by wrapping it about a plurality of filament binding posts so constructed as to automatically grasp and frictionally retain the corona wire at each turning point, and to enable the imposition of suitable tension on the wire without detracting from the ready removability of the wire in the event of replacement.